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Nitroxide Radicals as Hydrogen Bonding Acceptors. An Infrared and EPR Study.
Author(s) -
Franchi Paola,
Lucarini Marco,
Pedrielli Pamela,
Pedulli Gian Franco
Publication year - 2002
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/1439-7641(20020916)3:9<789::aid-cphc789>3.0.co;2-z
Subject(s) - electron paramagnetic resonance , chemistry , hydrogen bond , radical , nitroxide mediated radical polymerization , infrared spectroscopy , photochemistry , hyperfine structure , spectroscopy , solvent , hydrogen , molecule , organic chemistry , nuclear magnetic resonance , polymer , polymerization , radical polymerization , physics , quantum mechanics
The equilibrium constants for the formation of hydrogen‐bonded complexes with phenol, benzyl alcohol and diphenyl amine of a persistent nitroxide radical (TEMPO) have been measured for the first time by IR spectroscopy in solution. By making use of the data obtained with IR measurements it was possible to quantitatively determine the effect of hydrogen bonding on the nitrogen hyperfine‐splitting constant. On this basis it is shown that EPR spectroscopy can be used as an alternative to IR spectroscopy for the determination of the thermodynamic parameters of hydrogen bond formation with nitroxides by following the dependence of the experimental EPR nitrogen hyperfine splitting of these radicals upon changing the nature of the solvent. The experimental data obtained from both IR and EPR spectroscopy indicate that nitroxides are versatile hydrogen bond acceptors giving hydrogen bonds of strength similar to that of ethers or esters. The corresponding Abraham's β $\rm{_{2}^{H}}$ values have been determined as 0.46.